Most implantable medical devices, such as pacemakers and ICD's, use one or more implantable leads that electrically connect the medical device to a desired body tissue location. There are numerous types of implantable leads, just as there are numerous types of implantable medical devices. Implantable leads include epicardial leads, endocardial leads, atrial leads, ventricular leads, unipolar leads, bipolar leads, and the like. Representative of the many and varied types of leads that exist are those described, e.g., in U.S. Pat. Nos. 4,522,212; 4,649,938; 4,791,935; and 4,815,469; or as described by Furman, et. al, A Practice of Cardiac Pacing (Futura Pub. Co., Mt. Kisco, N.Y. 1986), e.g., at pp. 36-41.
All implantable leads include one or more electrodes at a distal end of the lead, and an electrical connector at a proximal end of the lead. The distal electrode is adapted to physically and/or electrically contact body tissue at a desired monitoring and/or stimulating location. Active or passive fixation means may also be included as part of the lead at or near the distal end in order to secure the electrode in its desired tissue-contacting location. The proximal connector is adapted to interface with the implantable medical device. Connecting the distal electrode to the proximal connector is the lead body. The lead body comprises one or more flexible electrical conductors, surrounded or otherwise protected by an appropriate insulating sheath, which establishes electrical connection between the distal electrode and the proximal connector. (Note: As used herein, and as is conventional when describing implantable leads, the "distal" end of a lead is the end farthest from the medical device, and the "proximal" end is the end closest to--usually the end connected to--the medical device).
When an implantable lead is first implanted in a patient, there are some preliminary electrical tests that should be performed before the lead is finally attached to its corresponding medical device. For example, if the lead is a pacing lead that is to be connected to an implantable pacemaker, then the lead is first implanted, e.g., transvenously, so that the distal electrode is in electrical contact with cardiac muscle tissue. Then, before the proximal connector of the lead is secured to the pacemaker, the proximal connector is temporarily connected to an appropriate testing device so that a series of stimulation pulses of varying energies, or other test signals (such as signals to measure the lead impedance), can be applied to the cardiac tissue through the lead in order to ascertain the capture threshold at which the cardiac muscle tissue contracts, or in order to determine other parameters associated with the lead. The results of such capture threshold testing, or other testing, advantageously provide an indication as to whether the distal electrode is making good contact with the body tissue, as well as what the initial setting of the stimulation energy of the pacemaker should be.
If the lead is a defibrillation lead that is to be connected to an implantable cardioverter-defibrillator (ICD), then typically at least two defibrillation leads are implanted so that the distal electrodes contact the appropriate cardiac tissue. The distal electrodes may comprise patch electrodes or any other appropriate defibrillation electrodes as disclosed, e.g., in U.S. Pat. Nos. 4,774,952; 4,817,634; 4,865,037; 4,991,603; or 4,998,975. The proximal connectors of such leads are then temporarily connected to an appropriate testing device, typically referred to as a "system analyzer", and the system analyzer then applies an appropriate signal (usually a low amplitude AC signal) to the defibrillation electrodes in order to induce fibrillation. Defibrillation pulses of varying energies are then applied to the cardiac tissue across the defibrillation electrodes in order to ascertain the defibrillation threshold, i.e., the amount of energy required in a defibrillation shock pulse in order to defibrillate the heart. Such defibrillation threshold is then used to guide the initial setting of the defibrillation energy generated by the ICD.
Proximal connectors used with most implantable leads are typically one of two types: unipolar or bipolar. Unipolar proximal connectors include a single proximal tip electrode (male connector) adapted to be inserted into an appropriate conductive annular ring or other receiving receptacle (female connector) located on or in the implantable medical device (or other testing device). Secure physical and electrical contact between the male and female connectors is typically obtained using a setscrew. That is, the setscrew is threadably mounted in the female connector and is tightened against the male connector so as to firmly hold it in physical and electrical contact with the female connector. In order for a proper connection to be made, it is necessary that the male connector and female connectors be of the same size.
Bipolar proximal connectors typically include a proximal tip electrode the same as is used in proximal unipolar connectors, and also include a proximal ring electrode, that is an annular conductive ring that is spaced-apart from the tip electrode. The receiving or female bipolar connector thus comprises an appropriate receiving channel having separate conductive elements therein that establish a secure physical and electrical connection with the proximal tip and ring electrodes of the lead. A setscrew, or equivalent, may also be used to secure one or both of the tip and ring electrodes within the female connector.
Some effort has been made in recent years to standardize the size of proximal connectors used with pacing leads, see, e.g., Calfee et al., "A Voluntary Standard for 3.2 mm Unipolar and Bipolar Pacemaker Leads and Connectors," Pace, Vol. 9, pp 1181-85, incorporated herein by reference. However, there still exists a wide variety of different sizes and types of proximal connectors that are used with implantable medical devices. Further, the size of proximal connectors used with defibrillation leads is typically different than the size of proximal connectors used with sensing/pacing leads. Hence, in order to connect the different sized proximal connectors to a system analyzer (or equivalent testing device) during the implant procedure, it has heretofore been necessary to use a plurality of cables, connector blocks, and/or a plurality of lead adapters for each size or type of proximal connector that may be encountered. See, e.g., U.S. Pat. No. 4,466,441 (in-line lead adapter).
Connection of implanted leads to a system analyzer in the prior art typically consists of two sets of cables and connector blocks; one for shocking and one for pacing functions. Each connector block of the prior art typically includes two female connectors to which two corresponding proximal male connectors of the implanted leads may be temporarily attached. Such temporary attachment is typically achieved by using setscrew connectors mounted to the connector block that receive and grip the male tips of the implanted leads. A cable, usually hard-wired to the connectors at one end and having a multi-pin connector at the other end, then provides the appropriate electrical interface between the connectors and the system analyzer. Unfortunately, the connectors used on such adapters are still size-dependent (i.e., there is no single female connector to which all sizes of proximal lead male connectors can be safely connected). Hence, different lead adapters must still be used for different sized leads. Thus, a substantial inventory of lead adapters must be maintained for use in the operating room where the implant procedure is being carried out. Further, any such adapters which are used must be sterile, which requires a separate sterilizing operation. Moreover, the use of such adapters increases the risk of damage and/or connection error. That is, the frequent connecting and disconnecting of the proximal connectors to and from the setscrew or other female connectors of the lead adapters, can, if not carefully carried out, damage the proximal connectors, particularly the delicate proximal ring electrode, thereby rendering the implanted lead unsuitable. Further, there is always the chance when leads are frequently disconnected and reconnected that an error will occur in the polarity of the connections that are made. Hence, there is a need in the art for a way to safely and efficiently connect the various sizes and types of proximal connectors existing on implanted leads to a system analyzer (or other testing device) used during the implant procedure, without the need of maintaining a large inventory of sterile lead adapters. That is, there is a need for a universal adapter that can be used with all implanted leads.
Further, when the implantable medical device is an ICD, it is desirable to test the performance of the ICD prior to finalizing its implantation, i.e., prior to sewing up the patient at the conclusion of the implant operation. This requires that the ICD be connected to the implanted leads at the same time that the system analyzer is connected to the ICD in order to monitor its performance, particularly to monitor the output energy delivered by the ICD. Typically, the state-of-the-art requires that such output energy monitoring can only be accomplished by using some sort of in-line lead adapter, e.g., a "Y" adapter that connects the output of the ICD to both the implanted defibrillation leads and to the system analyzer. The use of such adapter, which must be sterile, requires additional connecting and disconnecting of the implanted lead, which additional connecting and disconnecting may further damage the proximal male connector of the lead or the corresponding female connector of the ICD. Further, such additional connecting also increases the possibility that a connection of the incorrect polarity will be made. A connection of the improper polarity could, where large shocking energies are used by an ICD, easily damage the system analyzer and/or the ICD, and could be harmful to the patient. What is clearly needed, therefore, is a way to easily and safely test the performance of the ICD, including testing the output energy delivered by the ICD, after the defibrillation leads have been implanted and connected to the ICD. Accompanying this need is the need to perform such testing without the use of any special adapters that require additional disconnecting of the leads from the ICD and without the possibility of making a mistake in the polarity of the connection.
Thus, in summary, to minimize the risk of lead damage or polarity connection error, what is needed is an implant procedure or technique wherein the implanted leads may be detachably connected to the system analyzer without using setscrews or other holding mechanisms that could damage the leads; and wherein once the leads have been tested by the system analyzer, the leads may be connected to the ICD (or other medical device) just once, yet that still allows the ICD to be fully tested after the leads have been so connected, including the testing of the output energy delivered by the ICD, without concern for whether a proper polarity has been achieved between the ICD and the system analyzer.
The present invention advantageously addresses the above and other needs.